Firefox has a great Unity progress bar when stuff downloads. However, Thunderbird hasn't. (Or does it?)
Is there a Thunderbird progress bar available for Thunderbird?
The Firefox feature is integrated with the newest version of Ubuntu to date (12.04).
An add-on for Thunderbird was made during 11.04 days and that url can be found below:
This feature has been added into the Ubuntu Thunderbird build since and currently works (Ubuntu Thunderbird Version:
The download status bar feature is not a feature yet made in either the standard Ubuntu build or as a Thunderbird add-on at this point. Some ways to get this feature added to the next build of Ubuntu's Thunderbird would be by asking the question about a download status bar to the Ubuntu Mozilla Team here: https://answers.launchpad.net/ubuntu/+source/thunderbird/+addquestion
Another way to get this feature added would be to create an add-on for Thunderbird that would just help with the download status bar option for Unity and see if this feature will be added in the future (but can be used now if developed correctly).
Hope this helps.